Synthetic Metals (v.158, #15)

This study reports on the preparation of Pt- and Ru-based electrocatalysts through electrodeposition of Pt and Ru particles into the nanofibrous network of polyaniline (PANI)–poly(styrene sulfonic acid) (PSS). The sequence of electrodeposition of Pt and Ru particles was changed and the electrocatalysts, PANI–PSS–Pt–Ru and PANI–PSS–Ru–Pt, were obtained. Scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS), and cyclic voltammetry (CV) were employed to investigate the morphology, structural and electrochemical properties of the electrocatalysts, PANI–PSS–Pt–Ru and PANI–PSS–Ru–Pt. The distribution of Pt and Ru particles into PANI–PSS matrix was analyzed by the Auger depth profiles. The electrochemical behavior PANI–PSS–Pt–Ru and PANI–PSS–Ru –Pt and the electrocatalytic behavior toward oxidation of methanol were evaluated by cyclic voltammetry. PANI–PSS–Ru–Pt exhibited a superior electrocatalytic performance for methanol oxidation as compared to PANI–PSS–Pt–Ru.
Keywords: Polyaniline–poly(styrene sulfonic acid); Pt–Ru electrocatalyst; Deposition sequence; Methanol oxidation; Electrocatalytic activity;

A comparative study of the electrocatalytic oxidation of methanol is made in NaOH, Na2CO3 and NaHCO3 on bare Pt (Pt), polyaniline covered Pt (PANI) and Pt modified polyaniline film on Pt (Pt/PANI) using cyclic voltammetry, polarization, ac impedance spectroscopy and chronoamperometric techniques at 25 °C. The cyclic voltammetry and polarization studies show that the potentials at which methanol oxidation commences on different electrodes in each of the alkaline medium examined follow the trend Pt/PANI < Pt < PANI whereas the potentials for initiation of oxidation on each electrode in different alkaline media follow the order NaHCO3  > Na2CO3  > NaOH. The oxidation current is highest and charge transfer resistance lowest for Pt/PANI films compared to Pt in all the media studied. However, for the same Pt loading Pt/PANI films exhibit larger oxidation currents in NaOH followed by Na2CO3 and NaHCO3. The Tafel slope for methanol oxidation on Pt/PANI in NaOH, Na2CO3 and NaHCO3 has a value of about 115 mV decade−1. The chronoamperometric response of the Pt/PANI film at the peak potential for methanol oxidation shows lesser sensitivity to poisoning by CO compared to bare Pt and platinised Pt (Pt/Pt).
Keywords: Methanol oxidation; Alkaline medium; Polyaniline; Pt modification;

We have developed organic light-emitting devices using triphenylphosphine oxide (Ph3PO) layers. The operating voltage of device is substantially reduced by using a Ph3PO layer. For example, the required voltages for a current density of 20 mA/cm2 are 3.5 and 9.7 V for the devices with Ph3PO and Alq3 layers, respectively. Good electron transporting property of Ph3PO results in a high luminance of 1000 cd/m2 at a low driving voltage of 4.1 V in a device with a structure of ITO/2-TNATA (15 nm)/α-NPD:rubrene (1%, 10 nm)/α-NPD (30 nm)/Ph3PO (60 nm)/LiF (0.5 nm)/Al.
Keywords: Organic light-emitting device; Low voltage driving; Electron transport layer; Triphenylphosphine oxide; Ph3PO;

In this paper, the optical and electrochemical properties of sulphonated nickel phthalocyanine (NiPcSmix) were investigated. The ground state of spectra of NiPcSmix show splitting of Q band in DMF, but the fluorescence spectra have only one band, suggesting that only some component of the sulphonated NiPc fluoresce. Since, the organic materials are described on the basis of molecular orbital energies, i.e. highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) instead of valence band and conduction band. Such energies were estimated from cyclic voltammetry and optical absorption measurements. The dark current–voltage characteristics of ITO/NiPcSmix/Ag device in dark at room temperature shows a rectification behavior. At low voltages, current in forward direction was found to obey the diode equation, i.e. exponential increase in current with applied voltage and the conduction was controlled by thermionic emission mechanism. For relatively higher voltages, the conduction was dominated by a space charge limited conduction mechanism with single trap level of 0.34 eV. The JV characteristics in dark and the comparison of photoaction spectra of the device with the optical absorption spectra of NiPcSmix indicates the formation of Schottky barrier and Ohmic contact at Ag-NiPcSmix and ITO-NiPcSmix, respectively, in ITO/NiPcSmix/Ag device. The junction parameters such as built in potential, potential barrier height, carrier concentration and width of depletion layer were estimated from the capacitance–voltage (CV) measurement. The JV characteristic under illumination shows photovoltaic effect. The power conversion efficiency of the device has been improved upon thermal annealing attributed to the enhancement in the both crystallinity of NiPcSmix and charge carrier mobility due to the thermal treatment. We have also investigated the effect of PEDOT:PSS buffer layer in between ITO and NiPcSmix on electrical and photovoltaic properties of the device.
Keywords: Sulphonated NiPc; Space charge limited conduction; Electrical properties; Photovoltaic effect;

High dielectric constant polyaniline/poly(acrylic acid) composites prepared by in situ polymerization by Chao-Hsien Ho; Cheng-Dar Liu; Chia-Hung Hsieh; Kuo-Huang Hsieh; Sung-Nung Lee (630-637).
An ultra-high dielectric constant composite of polyaniline, PANI–DBSA/PAA, was synthesized using in situ polymerization of aniline in an aqueous dispersion of poly-acrylic acid (PAA) in the presence of dodecylbenzene sulfonate (DBSA). The water-soluble PAA served as a polymeric stabilizer, protecting the PANI particles from macroscopic aggregation. A very high dielectric constant of ca. 2.0 × 105 (at 1 kHz) was obtained for the composite containing 30% PANI by weight. The influence of the PANI content on the morphological, dielectric and electrical properties of the composites was investigated. The frequency dependence of dielectric permittivity, dielectric loss, loss tangent and electric modulus were analyzed in the frequency range from 0.5 kHz to 10 MHz. SEM micrograph revealed that composites with high PANI content (i.e., 20 wt%) consisted of numerous nano-scale PANI particles that were evenly distributed within the PAA matrix. The high dielectric constants of these composites were attributed to the sum of the small capacitors of the PANI particles.
Keywords: Ultra-high dielectric constant; Polyaniline composite; SEM morphology; Nano-scale PANI particle; Mini capacitor;

Preparation and electrochemical characterization of porous SWNT–PPy nanocomposite sheets for supercapacitor applications by Jiyoung Oh; Mikhail E. Kozlov; Bog Gi Kim; Hyung-Kook Kim; Ray H. Baughman; Yoon Hwae Hwang (638-641).
Highly porous sheets comprised of single walled carbon nanotubes and doped polypyrrole (SWNT–PPy) were prepared by vacuum filtration of SWNT–PPy methanol dispersions. The employed preparation procedure is an extension of conventional bucky-paper fabrication technique for the multi-component system. A number of nanocomposites with nominal SWNT:PPy compositions ranging from 1:0 to 1:1 were obtained and tested. Electrochemical properties of the nanocomposites were investigated by cyclic voltammetry and galvanostatic spectroscopy technique in aqueous 1 M NaCl electrolyte. The highest specific capacitance of 131 F/g was obtained for nanocomposite with 1:1 SWNT:PPy ratio. Prospective applications of prepared materials range from supercapacitors to electrodes for batteries and electromechanical actuators.
Keywords: SWNT–PPy; Cyclic voltammetry; Polymer;